This invention relates to instrumentation to measure and numerically display the distance from a point position of a conductor within a tooth to the peridontal membrane surrounding the tooth. More particularly, it relates to instrumentation to measure the actual length of a root canal in a tooth and the position of an electrically conductive probe in the canal with respect to the apical foramen of the root canal and provide the numerical display of the distance.
This invention specifically relates to the instrumentation to aid in the treatment of and cleaning out the root or roots of a tooth for which root canal nerve removal is necessary to prevent the loss of the tooth. Throughout this specification the term "instrument" includes a variety of devices used to insert into the tooth for direct treatment or as indirect aids in providing treatment, specifically including reamers, files and like instruments used to clean out the pulp of a tooth, pins, posts and like anchors fixed into the tooth, electrically conductive canal filing such as silver points, conductive plastic material and the like, syringe needles used to inject a filling into the root canal or another cavity, and like instruments. In the root canal cleaning process, it is necessary to use cleaning instruments to remove essentially all of the vital and non-vital pulp tissue, debris, and other contents of canal out of the root canal of the tooth all the way to, or at least close to, the apical foramen, referred to throughout as the apex. The position of an instrument in the pulp is extremely important as over-penetration through the apex through the peridontal membrane and into the tissue below the tooth is clearly over instrumentation. Pushing the instrument too far creates the risk of pressing contaminated contents of the canal into the periapical tissue and may result in excess root filling to an incorrect distance. Going too far in root canal preparation leads to patient suffering and undesirable side effects.
It is well recognized that the use of radiographs for the determination of the apex location is inadequate at best, leading to substantial errors and over instrumentation. In a Journal of Dentistry Research article, published April 1962, Vol. 41, No. 2, titled "Measurement of Root Canal Length, Imao Sanada discussed a new method using an apparatus " . . . to measure electrical resistance . . . " between an " . . . anode . . . inserted into the canal . . . " and a " . . . cathode . . . placed on the buccal mucous membrane, . . . ." The circuit was adjusted before each reading to a set current to calibrate the device. Dial readings on this type of instrument are not quantitatively distance readings. Subsequently, devices have been offered utilizing sounds to signal penetration position. Noboru Inoue described in his U.S. Pat. No. 3,660,901 an INSTRUMENT OF PROBING THE LENGTH OF A ROOT CANAL OF THE TOOTH, that issued May 9, 1972. Later a second sound was added to provide a reference standard against which the probe sound is compared. These devices are described in various papers and publications including A Clinical Evaluation of a Electronic Root Canal Measurement (Sono Explorer) by Captain Larry J. O'Neil, CPT DC, USA, presented to the Dental Educational Committee, Fort Sill, Okla., Mar. 25, 1973, and reprinted in Oral Surgery, Oral Med., Oral Pathology, Volume 38-number 3, pages 469-473, September 1974; an article entitled Clinical Evaluation of the Sono Explorer by John J. Plant, D.D.S., et al, published in The Journal of Endodontics, Volume 2, number 7, July 1976, pages 215 and 216; and an article entitled Determination of the Accuracy of the Sono-Explorer for Establishing Endodontic Measurement Control by Leigh R. Busch, published in The Journal of Endodontics, Volume 2, number 10, October 1976, pages 295-297, all the above incorporated herein by reference. A device is described in a publication dated Apr. 27, 1979, entitled Determining Root Canal Length by Noboru Inoue, et al, describing the Sono-Explorer Mark II including a description of circuit layout and operation incorporated herein by reference. Difficulties with the operation of these and similar devices have resulted in the problem of audible recognition of the sound changes necessary to be recognized as the instrument approaches the apex. Some of these devices have utilized the principle beat as frequency as the two wave forms approach a null condition to produce a clear tone as the probe approaches the apex. The device may be modified to produce a short period of silence when the sound waves cancel each other before the sound begins again as the probe is pushed past the apex. If the probe is moved too quickly, it will pass through the silence period and the beat on the opposite side of the apex sounds identical to that of the beat it had during the approach. Dials reading current passage do not measure distance. Therefore, over-instrumentation can occur. Lights have been employed to signal the approach of the probe to the apical foramen including U.S. Pat. No. 4,353,693 to Tibor Dery et al, issued Oct. 12, 1982, incorporated herein by reference. These lights provide an optical warning, but do not yield a measurement of the distance involved. Most endodontists prefer to approach the apex but not pierce it. Doctors differ as to best distance of penetration. While many doctors prefer to reach the apex, many doctors prefer only to reach the apical constriction in the canal generally located approximately 0.5 millimeters short of the apex. The prior art devices do not allow for this type of approach and do not provide for easy stopping short of the apex in this manner.
The present invention satisfies these needs and attains the objects provided herein as well as those that will be clear from the description of the invention.